Electrical-resistance device.



- H. S. MARTIN.

ELECTRICAL RESISTANCE DEVICE.

APPLIGATION FILED JULY 13, 1908.

Patented Apr. 27, 1909.

plied,

outrun s'rATEs PATENT OFFICE f HAROLD SHEEN MARTIN, OF LIVERPOOL,ENGLAND;

ELECTRICAL-RESISTANCE DEVICE. l t

To all whom it may concern:

Be it known that I, HAROLD SHEEN MAR- TIN, subject of the King of GreatBritain, residing at Liverpool, in the county of Lancaster, in theKingdom of England, have in-.

vented certain new and useful Improvements in Electrical-ResistanceDevices, of which the following is a description.

Thisinvention relates to an improved electrical resistance deviceadapted to be used for all purposes to which such devices areapotherwise to suit varyin requirements, for instance, when used in aamp circuit the device may be ad usted to vary the current flowingthrough the lamp and so permit a vanation in the amount of light givenby the lamp.

The resistance body consists of a mixture of the kind hereinafter morefully described, the resistance of which varies as the pressure exertedupon it is increased or decreased, the resistance being decreased whenthe pressure is increased. The mixture consists "essentially of aconducting material in granular or have been forced. springs which aredistorted when pressed powdered form and a non-conducting material inthe form of small scales. Suitable substances are gr'a bite for theconductor and mlca' for the insu ating material. There is mixed withthese two substances some other granular material, such for instance assand. It would appear that the decrease in the resistance' is producedby bringing the grains of theconducting material into intimate contactby means of applying pressure to the mixture, the increase in theresistance being brought about by the separation of the grains ofconducting material under the action of thelscales of insulatingmaterial, whichon the release of the pressure tend to move out of theconstrained positions into whichthey The scales of mica act as againstthe granular material (sand) 'infthe mixture. On the removal of thepressurethe flakes tend to return to their original positions movingaway from each other and carryin with them the powdered conducting ma=teria The proportions of the constituents of the mixture may vary widelydepending 1 on the purpose for which the resistance isto be used and therange of resistance and our rent-carrying capacity required; For-gin;-stance if a low resistance of comparatiyely Specification of LettersPatent. Application filed July 13,

the device being of the kind in which the resistance can be adjustedby'hand or Patented April 27, 1909'. 190s. Seria1No.443,208.-

small range is required the relative proportion of the graphiteandcontact surfaces is larger whereas, if higher resistance with greaterrange is required, these proportions will be reduced. As an example ofpropor- I tions which have been found in practice sat-7 given: I n

Powder graphite 2 grams by weight I Micafiakes 1. f Sand 7 1 I u u. u

sure plates of 12 Innis. diameter, gives a range of resistance of 73 to220,000 oh'ms.

drawin s which show one form of which t e resistance body is used.

In these drawings, Figure 1 is a vertical sectional view of the device,and Fig. 2" is a 'horizontal sectional view on line 22, Fig. 1.

or flakes of insulating material as forced into the constrainedposition, wherein the resistanceisdecreasedr The device consistsofahollow cylinder a at each end with a metal surfaces between which the'mixtureid is compressed, the other'surface being formed by means of adisk f at the end of a plunger carriedby a rod which is screw-threadeddescribed, for instance a pivoted lever having acam surface a used.

forrhfof device issuitable-for all ordi- 3 is an enlarged view, showingthe scales by. other means than 'by the means above isfactory'for some.purposes the following is I A quantity as: this. mam-re weighing" 4grams when placed between circular res-- now refer to the accompanyingdevlcein lined with insulating material I) and provided diskQ The disk'0 at the bottom of the cylinder forms one of the and ,worksthrough ascrew-threaded aper o ture in abridge piece .h located over the" otherend of the cylinder; The two co n1' pression'members c and f areconnected-to 1 pressingupon this disk may be 7 nary purposesvvhere'currents of normal magnitude are being dealt with. In caseshowever where very large currents are being ance.

dealt with, the surfaces of one or both of the pressure plates incontact with the material may be varied in' addition to the adjustmentof the pressure in order to adjust the resist- This may be eflected byforming one or both of these plates of a number of rings fitting one wihin the other, the number of which rings in contact with the mixture maybe varied as desired. The samelesult may be produced by formingthe plateor plates of a spring strip of metal which may e bent in such a mannerthat only part of it normally comes in contact with the mixture, theremaining. part however being pressed down against the material when itis desired to decrease the resistance.

'It is obvious that although specific forms ,of this device have beendescribed in detail,

considerable modifications may be made therein without departing fromthe invention.

In addition to graphite I can add rare earths which become conductorswhenheated. to certain temperatures, such as zirconia,

magnesia or thoria mixed with a largeor small proportion of another oxidor other substance, yttrium, cerium, orbium and didymium oxids, boricacid, calcium chlorid and tungstic acid. The eflect of heating isproduced in the passage graphite.

is with the object of increasing the currentcarrying capacity in aconducting body of of the initial current through the given bulk, andpreserving at the same time a high mitial resistance.

Ideclare that what I claim is:

1. An electrical resistance device comprising a resistance body in whichare inti mately mixed together a material in the form of springy scalesor flakes and a material in the form of grains.

2. An electrical resistance device com prising a resistance bodyconsisting of a mixture oia non-conducting material in the form of sprmscales or flakes, a granular material, an

3. An electrical resistance device comprising a resistance body in whichare intimately mixed together mica inthe form of my device by heatgenerated by The addition of these rare earths.-

a finely divided electrically con ,ducting material.

scales or flakes and a material in the form of grains.

4. An electrical resistance device comprising a resistance bodyconsisting of a mixture of mica in the form of scales or flakes, agranular material and a finely divided electrically conductin material.

5. 'An electrica resistance device comprisinga resistance bodyconsisting of a mixture of mica in the form of scales or flakes, a

-granular material, and finely divided graphite.

6. An electrical resistance device com- I prising a resistance bodyconsisting of a mixture of a non-conducting material in the form ofscales or flakes, a granular material, a finely divided conductingmaterial, and a material which becomes a conductor when heated to asuitable temperature.

7. An electrical resistance device consisting of a resistance body inwhich are inti mately mixed together a material in the form of s ringyscales orflakes and a material in the orm of grains, a receptacle forsaid body,

and means for varving the pressure upon 9. An electrical resistancedevice consisting of a resistance body in which are inti.

mately mixed together a material in the form of s ringy scales or flakesand a material in the orm of grains, a receptacle for said body, twoconducting plates dis osed opposite to each other in said receptac e,means for varying the distance apart of said plates, and

means for varying the conducting area in con tact with said body.

' In witness whereof, I have hereunto signed my name this 2nd day ofJuly 1908, in the presence of two subscribing witnesses.

HAROLD SHEEN MARTIN. Witnesses:

B10111). L. CLEAVER, WM. G. TRAVIS.

